Running lighting circuits in the loft space.

[Amp David]

When running lighting cables in the loft space, they can be clipped to the side of the joists no problem. When the cable then needs to be run at right angles to the joists, is it best pratice to drill the joists to pass the cable through or run over the top of them.

Cheers for the advice guys.

 

[Mark.W]

I've always drilled them mate to be honest

 

[Yooj]

I think the Building Regs only define notched or drilled joists when running perpendicular.

It is an interesting one, as the BR do not say you cannot...I can't recall whether one of the install methods in BS7671 would be suitable.

Yooj

 

[sparks1234]

Whats in the loft? how big are the joists? if they are 4x2 then thats going to be taking a lot out of them. can you not run the cables to the edge of the loft? or another way is to run a piece of timber across the existing timbers and clip to that

 

[snowiespark]

personlay i dont think its good idea to drill loft joists, keep cables to edges, lofts arent meant to even have stuf up there on new builds, so sure you cant drill new builds as they seem miminal spec...

 

[m4tty]

If your gonna drill the joists in the loft id make sure the holes are not bigger than they need be as your gonna affect the structural integrity holding the weight of the roof

 

[sparks1234]

I think you should assess the joists, i was in a loft of a 5 bed house yesterday, the main area they were 10 inch x 2 inch but over the master bed they were 3 inch x 1.5 inches, obviously you would not drill the smaller ones.

 

[saveloy]

Under no circumstances would I drill the joists on a truss type roof. These rooves are designed in such a way that any holes drilled could affect the structural integrity of the roof!

 

[Amp David]

Whats in the loft? how big are the joists? if they are 4x2 then thats going to be taking a lot out of them. can you not run the cables to the edge of the loft? or another way is to run a piece of timber across the existing timbers and clip to that

1910 terrace, they're only 3 1/4" x 2 1/4".

Think it would be best to take them to the edge before running the m accross the loft.

Thanks for the advice.

 

[Mark.W]

Agree with Sparks1234, best to assess the joists first.

 

[albi]

drilled the last one i did on a 1880 house mind you joists where 12inch x 3 inch a proper roof not like the NO SWEARING of today

 

[claret73]

this is something I questioned a while back...
It's Ok clipping them at the edges, but when you have to run at 90deg to drop into the light fitting access & they may then run over the joists, what then?

What if you leave it at that & the customer now wants to board it?

Saw a good one the other day. Rewired a Bungalow last year & have gone back intermittently to do a few light fittings etc. Went into loft & houseowner had double insulated & boarded with chipboard...Over all the cables!!

If you see that then, what responsibility do you have to that??

 

[sparks1234]

this is something I questioned a while back...
It's Ok clipping them at the edges, but when you have to run at 90deg to drop into the light fitting access & they may then run over the joists, what then?

What if you leave it at that & the customer now wants to board it?

Saw a good one the other day. Rewired a Bungalow last year & have gone back intermittently to do a few light fittings etc. Went into loft & houseowner had double insulated & boarded with chipboard...Over all the cables!!

If you see that then, what responsibility do you have to that??

You shouldnt be running them over joists where they may walk or board

 

[claret73]

Right, as an example...
did a rewire a couple of weeks back. Feed for the shower came up into loft. Run continued alongside the edge tucked up to rafters, then turned 90deg alongside a short wall. At that point dropped into shower isolator. From Isolator back up into loft it had to run across the joist to come down into a chase on the wall the customer had the shower on situated above the bath.

You can't drill or notch a shallow joist for a 10mm cable, I can't see how else this was going to run without crossing the joist??

Think next time I'll take some Pics & we can all colour our ideal runs...

 

[sparks1234]

Something like that I would screw a length of timber across the joists so that you can clip the cable to it so that it is not going to get walked on, or run the cable back to the edge, over the joist and then along it

 

[pushrod]

If you want to drill joists the holes should be centred and no more than 0.25 the depth of the joist in diameter. They should be positioned in the zone between 0.25 to 0.4 of the span from either end. (Regulation 522-12-03 of BS 7671) LINK

 

[chris murphy]

If you want to drill joists the holes should be centred and no more than 0.25 the depth of the joist in diameter. They should be positioned in the zone between 0.25 to 0.4 of the span from either end. (Regulation 522-12-03 of BS 7671) LINK

"Hello pushrod"


Without going to look at the British Standard or the Regulation that You have quoted I am fairly sure that what You quoted applies only to Floor Joists.

Even then Joists of less than 200mm [8"] should NOT be Drilled or Notched without additional reinforcement being applied to the Joists - for example 18 / 20 mm [3/4"] Ply being Laminated onto the sides of the Joists.

An example of NOT Drilling or Notching Joists of less than 200mm [8"] Deep is that Ground Floor Joists which are usually only about 100mm [4"] - as You know these should NEVER be Notched or Drilled - Even though these Joists will be supported on Wooden Plates and Brick Piers at regular intervals.

So although these 100mm / 4" Joists are well supported they should NOT be Drilled or Notched - It follows that a similar size Ceiling Joist which is only supported on the Room Walls [If Then] should NEVER be Drilled or Notched.

Ceiling `Joists` are usually part of the Roof Truss construction as was mentioned in previous Posts - So to ensure that the Roof Structure is NOT compromised under NO Circumstances should they be Drilled for Cables or Pipes.

Apart from weakening them in relation to the Roof Structure they would also be weakened with regard to walking across them when People have to access the Loft.

I have actually seen Ceiling Joists with Drill Holes in them for cables - the Homeowner had told the Electrician that they were going to Board Out the Loft Space - So the Electrician Drilled 25mm Holes right across the Loft - In the MIDDLE of the Span between the outside wall and the internal walls - to be close to the Room Lights in the Centre of the Rooms !

Imagine that on Ceiling Joists that were only 95mm X 47 mm [3 3/4" X 1 7/8"] !

Luckily I saw this as I am a fairly Big Man - I might well have been heavy enough to have these Drilled Ceiling Joists Break under My Weight !


Chris


P.S. - I am NOT `being funny` about noting the Metric and Imperial Measurements - the Imperial are what the Joists actually Measured - the Sizes of Wood that were used at the Time of Construction of the Houses.

 

[ackbarthestar]

The last couple of loft extensions were more or less top floor rewires where I ran and clipped the cables to the joists and then only hopped over the joist in the eves, never over the joists in the middle of the loft.
Another one was where there was a known extention going to be fitted at a later stage so ran the cables to the end of the joists and then clipped them up on the purlings so the cables were accessible and easy to move around while building work took place.

I was trained never to drill joists in the loft, particularly A framed structures, since they are not designed to carry the weight of a floor unless its a Victorian house where they are usually boarded out anyway.

edit: Generally as a ROT, any joist under 5" (125mm *50mm) should not be drilled.

Legh

 

[Engineer54]

Going by most of what you've been saying above, it's a wonder most of the houses over the years haven't collapsed on themselves.

Funny how all this this waffle was never thought of, or required in the past. Mind you, the older houses were made and built to last!! Can't see a lot of these modern homes passing the test of Time!! lol!!!

Most of these new rules (to me anyway) are just a load of hot air, dreamt up by those that have nothing better to do!! It would surprise me, if an electrician needed to drill a hole for cables to pass in a floor joist, it Will be drilled, and the cables will pass through that joist!! Come to that if a plumber needed to notch a joist for his pipework, it's going to get notched. ...It's the way of the World!! lol!!

 

[ackbarthestar]

- E54, You'll see holes and notches through most joists in older houses, but not, generally, in the loft !

 

[Engineer54]

- E54, You'll see holes and notches through most joists in older houses, but not, generally, in the loft !

Read my post again, did i say or mention loft joists?? Some of those older houses have loft joists, at least as big if not bigger in some cases than it's floor joists!! lol!!!

 

[ackbarthestar]

Read my post again, did i say or mention loft joists?? Some of those older houses have loft joists, at least as big if not bigger in some cases than it's floor joists!! lol!!!

I did, and you applied your argument generically whether drilled or notched, leaving it open !

edit: Plumbers don't usually notch or drill joists in loft spaces, unless they are bonkers

 

[ipf]

Once came across a situ where a loft joist had a 5'' complete cut out to allow the install of a recessed fitting. To make matters worse, a repeat on the same joist a couple of yards away. Probably even have had the mice cr****n' 'emselves.

 

[Engineer54]

I did, and you applied your argument generically whether drilled or notched, leaving it open !

edit: Plumbers don't usually notch or drill joists in loft spaces, unless they are bonkers

But i wasn't referring to your post, ...just that i'm not that quick at typing as most!!

How many plumbers do you know, ...that aren't Bonkers?? lol!!!

 

[chris murphy]

But i wasn't referring to your post, ...just that i'm not that quick at typing as most!!

How many plumbers do you know, ...that aren't Bonkers?? lol!!!

"Hello Engineer54",


I realise that You are Joking about Plumbers being Bonkers - words to that effect - But I have often seen references to Plumbers [Sometimes meaning Heating Installers / Engineers] that were less than Complimentary on the Forum.

I have definitely noticed that this does NOT seem to happen on Plumbers Forums regarding Electricians being even `Mildly Insulted`/ Refereed to in a less than Complimentary way.

Do You happen to know WHY this `Insult Plumbers` theme seems to happen on here ?

I am NOT being Over Sensitive here - I would definitely NOT take these comments seriously - I just wondered WHY they seem to be made so often ?

Having started My Career with a Plumbing Apprenticeship and then continued with further Training and Exams in Heating & Ventilation - Gas Utilisation - Electrical Installation - Defined Scope for Gas Installers / Heating Engineers etc. I am Certain that the Extent / Content / Time Scale of Training and Exams that I have taken is At Least Equal to MOST of the Electricians on here.

So I would state that I am in NO Way a Tradesman / Engineer with `Lesser Training` in MY Industry than an Electrician has in theirs.

I realise that the Electrical Trade / Industry is a Highly Technical Trade / Industry.

I wonder Why is it that some Electricians SEEM to be intimating that Plumbing / Plumbers [inc. Heating Engineers / Installers] are somehow in a `Less Technical Trade` / Industry ?

Some of the comments that I have read on the Forum seem to be directed at `Plumbers` [although the topic might be about Central Heating] as being somehow `Inferior Tradesmen` - Or that Plumbing [inc. Heating ?] is a `Lesser Trade` - ?

I definitely don`t want this to start a Row - I am just Intrigued about the comments that I have seen on here about Plumbers.


Regards,

Chris

 

[telectrix]

1910 terrace, they're only 3 1/4" x 2 1/4".

Think it would be best to take them to the edge before running the m accross the loft.

Thanks for the advice.

in an old house with a proper roof support structure as opposed to the modern trusses, the ceiling joists are there solely to support the ceiling. these can be drilled sendibly without affecting the strength of the structure. however, i consider it good practice to route the cables towards the eaves when running at right angles to the joists. they are also then out of the way of mr. joe public's size 10's.

 

[mackers]

as said if trusses DO NOT DRILL . also as said try keep away from areas likley to be used for storage/access. also bare in mind loft insulation as this has a great detrement to the cable loadings. to be fare in the 20 + years i been a spark can,t remember joist been drilled in any loft ive been in ,most are 3x2 unless designed for dormers.
only time i drilled a truss was when i was an apprentice and got the mother of all -------ings LOL

 

[Dan the spark]

Wouldn't advise drilling the joists in a loft, just run the cables where no one is gonna tread or put things on:builder:

 

[Deleted member 26818]

The joist in lofts, are there as far as I'm aware, to fix the ceiling to.
They are not generally structural.
Yes crtain pre-formed trusses are structural, and it may not be possible to drill those.
I would would suggest contacting either building control or a structural engineer in such circumstances.
Remember, that cables if run through joists should be at leat 50mm from the surface of the ceiling or floor, or provided with mechanical protection.

 

[Specialist]

Long time since I studied this, but I think you'll find that the the Loft joists make up part of the Structural Integrity of the roof & holding the ceiling up is secondary.
The Trusses (Rafters) & ceiling joists make up an A frame structure, what happens when you remove the crossbar from an A frame & then load weight onto it ? It collapses.

 

[chris murphy]

in an old house with a proper roof support structure as opposed to the modern trusses, the ceiling joists are there solely to support the ceiling. these can be drilled sendibly without affecting the strength of the structure. however, i consider it good practice to route the cables towards the eaves when running at right angles to the joists. they are also then out of the way of mr. joe public's size 10's.

"Hello telectrix",


Without wanting to seem argumentative - even in the example that you mention where the Ceiling Joists are NOT part of the Roof Structure - would it not be the SIZE of the `Ceiling Joists` that SHOULD prevent People Drilling or Notching them ?

As in My previous example where the Ceiling Joists were a `Typical Size` of approx. 95mm X 47mm - How could it EVER be justified to Drill these Ceiling Joists ? - a 20mm or 25mm Hole in the Centre of a 95mm piece of Timber - ?


Chris

 

[High Tower]

Chris,

There will always be a amount of bitching about other trades no matter what!!, and plumbers are probably the closest to us in the job they do, and often plumbers are on site for first and second fix around the same time as us.

on the same note, for every good conciencious plumber, there are 5 more arrogant careless clowns that have no clue about anything other than pipes!!. how many times do we have to have cables drilled and screwed by muppets with no clue or knowledge of cable zones, had bonding conductors removed and not replaced, had pipes run close to cables then expected to move cables. and don't even start me on part p plumbers!

Chris, you are a exception to the rules mate! if more people took the interest and made the effort that you do!, we would be much better off

 

[41steve]

just installed mine, no problem. clip them to the side of the timbers. i dont want a pointed ceiling so i have studded from the apex to make a flat area in the roof, looks so much better an plenty of room to keep cables in the correct zones.

 

[ample current]

Getting away a little from how we get accross the joist in a loft space how do we run the cables with so much insulation in them, nowadays 300mm, so well above the tops of the joists? say any suggestions aof where to clip the cables here

 

[41steve]

the insulation i am using is iso super 10. its clipped to the underside of the joists. thats architects 4 ya! channel the cables?

 

[41steve]

the insulation i am using is iso super 10. its clipped to the underside of the joists. thats architects 4 ya! channel the cables?

those timbers have to carry the weight of the roof! i dont think an hole in a 4x2 would comply anyway.

 

[chris murphy]

Chris,

There will always be a amount of bitching about other trades no matter what!!, and plumbers are probably the closest to us in the job they do, and often plumbers are on site for first and second fix around the same time as us.

on the same note, for every good conciencious plumber, there are 5 more arrogant careless clowns that have no clue about anything other than pipes!!. how many times do we have to have cables drilled and screwed by muppets with no clue or knowledge of cable zones, had bonding conductors removed and not replaced, had pipes run close to cables then expected to move cables. and don't even start me on part p plumbers!

Chris, you are a exception to the rules mate! if more people took the interest and made the effort that you do!, we would be much better off

"Hello High Tower",

Thank You for your reply and your complimentary remarks about Me.

I realise that there can be conflict between our Trades because of the situation that You mentioned regarding being on Site at about the same times for our First and Second Fix Works - But I must have been Lucky as I have not Personally encountered any problems working on site with Electricians - obviously I have been Working with considerate Tradesmen and I am definitely considerate of their Works.

I definitely do think about the `Following Trades` - usually an Electrician - and also I would NOT want ANYONE to be able to Critisise anything about My Workmanship.


I would be `Horrified` to think that something that I did Carelessly either Damaged another Tradesman`s Work - Or affected the Installation of His Work in a Detrimental way !

Because I have previously had a lot of experience in taking on entire refurbishments where I would have been not only the Heating, Plumbing and Gas Installer but also the Main Contractor - So at no time would I want to do anything that would affect another Trades Work.

But I would have been VERY Considerate of other Trades Work / Cable Routes etc. [Guessed or Asked about] from the time of being an Apprentice.


I would guess that what You describe happens mostly on Domestic Refurbishments / Conversions etc. [?]

I have also had a fair bit of experience in Supervisory Positions on Site - with as many as 60 Plumbers - Heating Engineers & Apprentices - these were Contracts on Large Sites with obviously Electrical Contractors and all other Trades on Site.

I have NOT experienced much `Plumber / Electrician` Rivalry / Animosity on these Large Sites - Just problems over the Contract Programs putting the Two Trades into the same location at the same times.

I am Sorry to hear that some / most of the Electricians have had BAD Experiences with `Plumbers` while Working - Your Quote about there being a 5 to 1 ratio of Careless / Inconsiderate Plumbers to the Good / Considerate Plumbers is really Shocking [No Pun intended] to Me !


Thanks Again for your reply.

Regards,

Chris

 

[pushrod]

"Hello pushrod"


Without going to look at the British Standard or the Regulation that You have quoted I am fairly sure that what You quoted applies only to Floor Joists.
.

Hi Chris, if you do go to the reg i quoted ( i see the link i put in no longer works) you will see that it does in fact mention both floors and ceilings - as it does in the electricians guide to the building regs and GN1. It is now 522.6.100 in ammendment 1. The sensible thing is always to assess the situation and in lofts the prevalence of insulation would usually usually make it sense to look for an alternative route if you don't want to seriously derate your CCC.

 

[chris murphy]

Hi Chris, if you do go to the reg i quoted ( i see the link i put in no longer works) you will see that it does in fact mention both floors and ceilings - as it does in the electricians guide to the building regs and GN1. It is now 522.6.100 in ammendment 1. The sensible thing is always to assess the situation and in lofts the prevalence of insulation would usually usually make it sense to look for an alternative route if you don't want to seriously derate your CCC.

"Hello pushrod",

Thanks for letting Me know about the Regulation Detail.

This comment is NOT Me trying to be `Funny`/ Sarcastic - in ANY Way so Please don`t be offended - I would NOT have to look up ANY Regulation - Building Regulation or any other to decide that I would NEVER Drill or Notch ANY Joist or other Timber that was much less than approx. 200 mm Deep.

This Figure is based on an 8" Joist with a Notch of 25mm for a 22 mm Pipe - which is `No More than One Eighth of the Depth of the Joist` - obviously for practical purposes the 25 mm Notch might be a couple of Millimetres deeper to ensure that the Pipe does stay beneath the top of the Joist level - but still a very small percentage over that recommended Depth of Notch.

As I have known this figure for 40 Years - I cannot readily give a reference for it.

This is almost impossible to adhere to when you are running 28 mm Pipes - as the 8" Joist is the most prevelent Joist Depth - then the Joist will have to be Notched to perhaps 32 mm - Nothing else can be done in these circumstances - As Building Control would know and have to accept - Unless they insisted that the Joists were Reinforced by Laminating Ply onto the sides - which would be within their remit - BUT would be excessive in My opinion.

I know that when Drilling a Joist different figures apply in relation to the Hole Size / Depth of Joist - as when Drilling the `Neutral Axis` the `One Eighth of Joist Depth` does NOT Apply - But I would Personally NOT be wanting to Drill a Joist that was smaller than 200 mm Deep.


I also realise that Cable Routes / Considerations differ from those for Pipes when planning the route.


Our Professional Judgement would also allow Us to decide whether a Joist or other Timber could be Drilled or Notched WITHOUT a Risk of Structural Failure from Loads etc.


Regards,


Chris.


"Happy Christmas and New Year" - to You and All of the Members on the Forum

 

[Amp David]

I've always wondered how those joists manage to carry all that new insulation they stick up there nowadays :carolers:

 

[chris murphy]

I've always wondered how those joists manage to carry all that new insulation they stick up there nowadays :carolers:

"Hello Amp David",


You might remember [as You replied to Me] that I enquired about Electrical Cables being affected by Loft Insulation prior to one of My Relatives having their Loft Insulated with 270 mm of Fibre Glass Blanket Insulation.

The Loft has been Insulated now and My Relative is disappointed with how much the Loft Space has been `diminished` in relation to what they had thought would be `Left`.

They thought that they would be able to just Lay Down some Boards on top of the Loft Insulation wherever they liked and put items onto those Boards - Until I told them that it is the Thickness / Air Space within the Thickness of the Fibre Glass Blanket Insulation that actually forms the Insulating `Barrier` - and that `Flattening` the Insulation would negate the Full effectiveness of the Insulation.

I told them to actually Insulate the area where they wanted to board for storage [Small Amount of 100 mm Blanket Insulation between Ceiling Joists ] - Board it out - and that the Loft Insulators would then Overlay the 170 mm `Top Layer` onto the Boards which My Relatives could then move to Store items - When they wanted to do so.

They did the 100 mm Insulation between the Ceiling Joists and used Loft Boards to Board an area in the Loft Space.

The Loft Insulators refused to Overlay the Boarding - Until My Relative telephoned Me and asked them to explain the reason to Me - When I explained My Profession and My Knowledge of Heat Loss / Insulation to them and told them that there was NO Reason to Refuse to Overlay the Boarding - they then reluctantly agreed to Overlay the Boarding.


I had mentioned the Difficulties of accessing areas of the Loft Space AFTER the Loft Insulation - but People don`t realise exactly HOW Difficult / Dangerous this can be until they actually SEE what the Loft looks like after it has been Insulated.


Regards,

Chris

 

[ackbarthestar]

I think there are other ways of insulating loft spaces and saving lots of space, such as the use of solid 'foam' cut to fit between the rafters and then covered with aluminum 'bubble wrap'

 

[chris murphy]

I think there are other ways of insulating loft spaces and saving lots of space, such as the use of solid 'foam' cut to fit between the rafters and then covered with aluminum 'bubble wrap'

"Hello ackbarthestar",


I think that We discussed this in the other Thread where I went into a LOT of detail about Loft Insulation:


If you `Insulate` between the Rafters as You describe in your Post - Unless the Loft is going to be Converted into Living Space the Temperature of the Loft would still be Very Cold regarding the Ventilation / Advantitious Ventilation.

The Ventilation - either purpose provided OR Accidental / Adventitious means that the AIR in the Loft Space would be almost as Cold as the Outside Temperature - You would still be Losing the Heat from your Rooms into the Loft Area - Because of the Insulation in the Rafters you would now be Heating the Loft Area with the `Heat Loss` from the Home.

Regards,

Chris

 

[ackbarthestar]

Good point about ventilation, however, this method can also be applied between the loft joists and then boarded over if necessary.

 

[chris murphy]

Good point about ventilation, however, this method can also be applied between the loft joists and then boarded over if necessary.

"Hello Again ackbarthestar",

Good Idea - But I believe that this Sheet Type Insulation is VASTLY Expensive - I would hate to think how much it would Cost - even for My Loft Space which is approx. 100 SQ. Metres - ?

I have also been told that the Sheets are NOT the Ideal Width for putting between the Rafters OR Joists - meaning a LOT of Off Cuts - On VERY Expensive Sheet Insulation !

Obviously If the Cost was Not a problem this type of Loft Insulation would probably be the BEST regarding what You mentioned about Boarding Over the Joists - The required Insulation Rating within an approximately 100 mm Joist Depth.



"Happy Christmas and New Year" to You.


Chris

 

[ackbarthestar]

"Hello Again ackbarthestar",

Good Idea - But I believe that this Sheet Type Insulation is VASTLY Expensive - I would hate to think how much it would Cost - even for My Loft Space which is approx. 100 SQ. Metres - ?

I have also been told that the Sheets are NOT the Ideal Width for putting between the Rafters OR Joists - meaning a LOT of Off Cuts - On VERY Expensive Sheet Insulation !

Obviously If the Cost was Not a problem this type of Loft Insulation would probably be the BEST regarding what You mentioned about Boarding Over the Joists - The required Insulation Rating within an approximately 100 mm Joist Depth.



"Happy Christmas and New Year" to You.


Chris

Its about £60 per roll and 1 - 2 rolls with sealing tape will cover more of less any reasonably sized loft space... Its also good for space explorers !

 

[41steve]

soz, i was on about electrics for a loft conversion. i ment to say trusses an not joists!

 

[chris murphy]

Its about £60 per roll and 1 - 2 rolls with sealing tape will cover more of less any reasonably sized loft space... Its also good for space explorers !

"Hello ackbarthestar",

I am a bit confused now - when You mentioned the `Solid Foam` Insulation in this comment:

`I think there are other ways of insulating loft spaces and saving lots of space, such as the use of solid 'foam' cut to fit between the rafters and then covered with aluminum 'bubble wrap'



I thought that You meant the SHEETS of Foam Insulation - Perhaps sold in sizes something like 1200 mm X 600 mm X 50 mm - Foil Sheet applied to both sides.

It was this type of Sheet Insulation that I meant was VERY Expensive.


Chris

 

[robsparky1975]

soild foam,is it celotex you mean?

 

[Mr.Si]

soild foam,is it celotex you mean?

That is what I thought it meant too.

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